Sarah Marriott, 32, kissed one-week-old Sebastian Blenkinsop as his life support machine was turned off.
She later read the words of a children's story "Guess How Much I Love You" to her little boy as he slipped away.
Sarah and her partner Jonathon Blenkinsop, 31, had to make the decision to switch off their son's life support machine when he became ill after birth.
Seb had suffered from a genetic condition called Alveolar Capillary Dysplasia (ACD), which has been diagnosed in just four children in England.
The mother said: "We just kept telling him how much we loved him, kissing him, saying sorry for not being able to prevent it and that we wished it could have been different."
Seb was born by emergency caesarian section weighing 4lb 13oz at 11.07am on 2 April, 2015, at the University Hospital of North Tees in Stockton.
Within hours, he was struggling to breathe and was transferred to the Freeman Hospital, Newcastle, and placed on life support to rest his organs while tests were carried out.
Marriott was only able to go and be with her son after needing to stay in recovery at North Tees for two days.
Five days after he was born, Marriott and Blenkinsop were told that Seb was suffering fits and had bleeding on his brain and severe brain damage.
They were advised that the best option was to turn off the machine.
Seb's life support was switched off at 11.07am on 9 April 2015 - one week after he was born.
He passed away while Marriott sang him to sleep with the poignant words of a children's book by Sam McBratney.
The final line reads: "I love you right up to the moon - and back."
The couple have now launched an appeal to raise funds for further research into the condition which claimed their son.
Marriott, who works in recruitment, said: "I kissed him and read a book called Guess How Much I Love You to him as he died, about two hares.
"He had the little hare teddy with him the whole time.
"I knew it was the best thing for him, and it felt like a relief for him that he wasn't going through anymore pain or machines pumping medicines into him.
"After he passed and the machines were disconnected, we bathed him and finally used some of his own clothing and dressed him for the first time."
She added: "It's still so emotional. Within 30 seconds of waking up I cry. I think about him all day. I sleep with his little hare teddy every night - it makes me feel closer to him."
Marriott, of Rift House, Hartlepool, says one complication of her pregnancy was that she was carrying excess fluid.
Carrying excess fluid can mean nothing or it can indicate that the mother has an infection or that something is wrong with the baby.
But rigorous checks by medics did not pick up little Seb's illness and the mother was reassured her baby was fine.
ACD affects the development of the lungs and their blood vessels which prevents the heart from developing properly, but forces it to pump harder.
Without a lung transplantation, infants with ACD have not been known to survive past one year of age, and most affected infants live only a few weeks.
The parents are now due to have DNA testing by a medical research doctor in the US to help uncover answers about the condition, which has only been diagnosed in 200 infants worldwide.
They are also working with other affected families in an attempt to fund research.
Marriott, who is also mum to two children from a previous relationship - Seb's sister Sadie, 12 and brother Kori, 9, said: "Seb just looked like a perfect newborn when he was born.
"It sounds cheesy and corny but I never thought anything like this would happen to me or my baby, it's like something that you read in magazines. I felt just like a robot.
"It was so hard getting told what they were doing to him at the post mortem but we knew it was the right thing to do otherwise we would never know what was wrong and research can't be done otherwise.
"But it felt like he had already been through so much. I wanted to blame somebody but after looking into this condition, there is nobody to blame.
"The only thing we can do it try to help get it researched so that one day it can help. I'm up and down every day. It still doesn't feel like it's happened."
Sarah and Jonathan, a plumber, are now working with the David Ashwell Foundation, which is run by a family in Middlesbrough whose baby died from ACD.
The charity has raised £1400,000 since March 2011 and has already funded two studies, with a further three studies going ahead in 2015.
To donate and for further information visit uk.virginmoneygiving.com/SomeoneSpecial/Sebblenkinsop or www.facebook.com/Seb.blenkinsop.